Nowadays, an individual identification technology using wireless communication has attracted attention. In particular, as a semiconductor device which communicates data by wireless communication, an individual identification technology using an RFID (Radio Frequency Identification) tag has attracted attention. The RFID tag is also called an IC (Integrated Circuit) tag, an IC chip, an RF tag, a wireless tag, or an electronic tag. The individual identification technology using an RFID tag has started to help production of an individual object or management, and has been developed to be applied to personal authentication.
Among RFID tags, there is a semiconductor device which communicates data by electromagnetic induction (Reference 1: Japanese Published Patent Application No. H11-11058). A conventional semiconductor device is described with reference to FIG. 2.
A semiconductor device 301 which communicates data by electromagnetic induction includes a coiled antenna 302 and a semiconductor integrated circuit 303 connected to the coiled antenna 302. Note that as shown by dotted lines in FIG. 2, a terminal 331a of the semiconductor integrated circuit 303 is connected to one end 332a of the coiled antenna 302, and a terminal 331b of the semiconductor integrated circuit 303 is connected to the other end 332b of the coiled antenna 302.
When the semiconductor device 301 is brought close to a coiled antenna connected to a reader/writer, an AC magnetic field is generated from the coiled antenna connected to the reader/writer. The AC magnetic field passes through the coiled antenna 302 in the semiconductor device 301, and electromotive force is generated between the terminals (between the one end 332a and the other end 332b) of the coiled antenna 302 in the semiconductor device 301 by electromagnetic induction. The semiconductor integrated circuit 303 in the semiconductor device 301 is operated by electromotive force.
In the conventional semiconductor device 301 which communicates data by using electromagnetic induction, the coiled antenna 302 and the semiconductor integrated circuit 303 do not overlap with each other. Here, the fact that the coiled antenna and the semiconductor integrated circuit do not overlap with each other means that the semiconductor integrated circuit and a portion of a wiring, which forms a coil of the coiled antenna do not overlap with each other when viewed from a direction parallel to a central axis of the coiled antenna. The portion of the wiring, which forms the coil of the antenna means that portions of a wiring provided adjacent to each other at regular intervals in the antenna. Note that the semiconductor integrated circuit includes not only an element which forms a circuit but also a power source line, a leading wiring, or the like. In addition, in the conventional semiconductor device 301, the semiconductor integrated circuit 303 is arranged inside the coil of the coiled antenna 302. Accordingly, an area of a portion (referred to as a region 300 in FIG. 2) inside the coil of the coiled antenna 302, in which the semiconductor integrated circuit 303 is not formed is small. Thus, a magnetic flux which passes through the coiled antenna 302 in the aforementioned AC magnetic field is small. Therefore, since sensitivity of the antenna decreases, electromotive force generated by electromagnetic induction is small. Since electromotive force is small, there is a possibility that the semiconductor integrated circuit 303 is not operated.
In addition, even when electromotive force with a degree that the semiconductor integrated circuit 303 to operate is obtained, in a case where electromotive force is small, momentary variation of electromotive force due to noise or the like affects significantly, and electromotive force is momentarily decreased, so that the semiconductor integrated circuit 303 would not be operated.
Note that, in order to ensure an area of a portion inside the coil of the coiled antenna 302, in which the semiconductor integrated circuit 303 is not formed, there is a method in which a semiconductor integrated circuit is provided outside a coiled antenna. However, this method leads to make a large semiconductor device.
In view of the situation above, with respect to a semiconductor device which communicates data by wireless communication, an object of the present invention is to improve sensitivity of an antenna and to protect a semiconductor integrated circuit from noise or the like without increasing the size of the semiconductor device.
The present invention is a semiconductor device including the following structure in order to solve the problems described above.
A semiconductor device of the present invention includes a coiled antenna (including a loop antenna and a spiral antenna) and a semiconductor integrated circuit which is electrically connected to the coiled antenna. The semiconductor integrated circuit is arranged so as to overlap with the coiled antenna.
A semiconductor device of the present invention includes a circular coiled antenna and a semiconductor integrated circuit which is electrically connected to the coiled antenna. The semiconductor integrated circuit is arranged so as to overlap with the circular coiled antenna.
A semiconductor device of the present invention includes a triangular coiled antenna and a semiconductor integrated circuit which is electrically connected to the coiled antenna. The semiconductor integrated circuit is arranged so as to overlap with at least one side of the triangular coiled antenna. Note that the semiconductor device may be arranged so as to overlap with one side of the triangular coiled antenna and not to overlap with the other sides thereof.
A semiconductor device of the present invention includes a square coiled antenna and a semiconductor integrated circuit which is electrically connected to the coiled antenna. The semiconductor integrated circuit is arranged so as to overlap with at least one side of the square coiled antenna. Note that the semiconductor integrated circuit may be arranged so as to overlap with one side of the square coiled antenna and not to overlap with the other sides thereof.
A semiconductor device of the present invention includes a polygonal coiled antenna and a semiconductor integrated circuit which is electrically connected to the coiled antenna. The semiconductor integrated circuit is arranged so as to overlap with at least one side of the polygonal coiled antenna. Note that the semiconductor integrated circuit may be arranged so as to overlap with one side of the polygonal coiled antenna and not to overlap with the other sides thereof.
Here, the fact that the coiled antenna and the semiconductor integrated circuit overlap with each other means that the semiconductor integrated circuit and a portion of a wiring, which forms a coil of the coiled antenna overlap with each other when viewed from a direction parallel to a central axis of the coiled antenna. The portion of the wiring, which forms the coil of the antenna means that portions of a wiring provided adjacent to each other at regular intervals in the antenna. Note that the semiconductor integrated circuit includes not only an element which forms a circuit but also a power source line, a leading wiring, or the like.
The semiconductor integrated circuit is operated by electromotive force generated by electromagnetic induction in the coiled antenna as power source voltage.
In a semiconductor device of the present invention, a transistor is not necessarily included in a region where a coiled antenna in a semiconductor integrated circuit overlaps with the semiconductor integrated circuit. Note that at least a channel forming region of a transistor is not included in the region where the coiled antenna in the semiconductor integrated circuit overlaps with the semiconductor integrated circuit.
In addition, a semiconductor device of the present invention may include a digital circuit and an analog circuit, and the digital circuit may be arranged in a region where the coiled antenna in the semiconductor integrated circuit overlaps with the semiconductor integrated circuit.
Further, a semiconductor device of the present invention includes a capacitor in a region where the semiconductor integrated circuit overlaps with the coiled antenna.
The capacitor may be electrically connected to the antenna. The capacitor may be a resonant capacitor connected to the coiled antenna in parallel. The resonant capacitor is a capacitor, and the capacitor and the coiled antenna form a resonance circuit.
In addition, the capacitor may be a storage capacitor for holding power source voltage of the semiconductor integrated circuit.
Note that the capacitor may be one of elements included in the semiconductor integrated circuit.
Alternatively, the capacitor may have a structure in which a part of a wiring of the coiled antenna is used as one electrode, a part of a wiring of or an electrode of the semiconductor integrated circuit is used as the other electrode, and an insulating film is sandwiched between the one electrode and the other electrode. The other electrode may be a part of a wiring in the semiconductor integrated circuit, in which a predetermined potential is held. In addition, the other electrode may be a power source line of the semiconductor integrated circuit. The power source line may be arranged so as to surround an element included in the semiconductor integrated circuit. Note that the potential of the power source line needs to be kept at a predetermined level when a radio signal is supplied to the semiconductor device.
Note that the coiled antenna and the semiconductor integrated circuit may be separately formed over different substrates to be attached to each other or may be formed over one substrate.
The number of windings of the coiled antenna may be one or more.
The semiconductor integrated circuit may be formed over a single crystal semiconductor substrate such as a silicon wafer or may be formed over an insulating substrate by using a thin film transistor.
An active layer of the thin film transistor may be formed of an amorphous semiconductor or may be formed of a crystalline semiconductor.
A semiconductor device of the present invention includes a coiled antenna and a semiconductor integrated circuit which is electrically connected to the coiled antenna, and the semiconductor integrated circuit is arranged so as to overlap with the coiled antenna. In addition, in a case where the coiled antenna is square, triangular, or polygonal, a semiconductor integrated circuit is arranged so as to overlap with one side of the coiled antenna and not to overlap with the other sides of them. Therefore, compared to a case where a coiled antenna is not overlapped with a semiconductor integrated circuit as is conventional, an area of a portion inside a coil of a coiled antenna, in which a semiconductor integrated circuit is not formed can be enlarged.
Thus, in an AC magnetic field generated from an antenna connected to a reader/writer, a magnetic flux which passes through a coiled antenna can be increased. Therefore, electromotive force generated by electromagnetic induction can be increased. As for a semiconductor device of the present invention, since electromotive force is increased, a semiconductor integrated circuit is easily operated. Thus, arrangement of the coiled antenna and the semiconductor integrated circuit in the semiconductor device is devised, so that sensitivity of the antenna can be improved and power enough to operate the semiconductor integrated circuit can be obtained without increasing the size of the device. In addition, a communication distance can be improved.
Further, a structure in which a transistor (at least a channel forming region of the transistor) is not included in a region where a coiled antenna overlaps with the semiconductor integrated circuit is used. In this manner, when the coiled antenna communicates, a direct effect on a transistor due to noise on a signal or the like or variation of electromotive force generated by electromagnetic induction or the like can be suppressed and malfunction of a semiconductor integrated circuit can be reduced.
In addition, a semiconductor device of the present invention may have a structure in which a digital circuit and an analog circuit are included and the digital circuit is arranged in a region where a coiled antenna overlaps with the semiconductor integrated circuit. The digital circuit is less affected by noise than the analog circuit. Therefore, by arranging the digital circuit in the region where the coiled antenna overlaps with the semiconductor integrated circuit, a semiconductor device can be downsized and malfunction of the semiconductor integrated circuit can be reduced.
Furthermore, a semiconductor device of the present invention includes a capacitor in a region where a semiconductor integrated circuit overlaps with a coiled antenna. The capacitor can suppress an absolute value of change in the potential due to variation of electromotive force caused by noise or the like. That is, the momentary variation of electromotive force due to noise or the like can be mitigated, and the semiconductor integrated circuit can be easily operated.
In addition, by providing a capacitor to be a resonant capacitor in a region where a semiconductor integrated circuit overlaps with a coiled antenna, a semiconductor device can be further downsized.
Note that by providing the capacitor included in the semiconductor integrated circuit in the region where the semiconductor integrated circuit overlaps with the coiled antenna, the semiconductor device can be further downsized as well as an advantage that the momentary variation of electromotive force due to the aforementioned noise or the like can be mitigated.
Alternatively, the capacitor can have a structure in which a part of a wiring of a coiled antenna is used as one electrode, a part of a wiring of or an electrode of a semiconductor integrated circuit is used as the other electrode, and an insulating film is sandwiched between the one electrode and the other electrode. The other electrode may be a part of a wiring in the semiconductor integrated circuit, in which a predetermined potential is held. The wiring in which the predetermined potential is held may be a power source line of the semiconductor integrated circuit. Accordingly, without increasing the number of wirings, a capacitor can be formed in a region where the semiconductor integrated circuit overlaps with the coiled antenna.
Moreover, the power source line may be arranged so as to surround an element included in the semiconductor integrated circuit. In this manner, the semiconductor integrated circuit can be shielded from noise outside the circuit or the like and the momentary variation of electromotive force due to noise or the like can be mitigated, and reliability of the semiconductor integrated circuit can be enhanced.
Note that the coiled antenna and the semiconductor integrated circuit may be separately formed over different substrates to be attached to each other or may be formed over one substrate. In particular, in the case where the coiled antenna and the semiconductor integrated circuit are formed over one substrate, distance between a wiring of the coiled antenna and an electrode or wiring of the semiconductor integrated circuit can be set short. Therefore, in the case of providing a capacitor having a structure in which a part of a wiring of the coiled antenna is used as one electrode, an electrode or a part of a wiring of the semiconductor integrated circuit is used as the other electrode, and an insulating film is sandwiched between the one electrode and the other electrode; area of the electrode in the capacitor can be small, and providing the capacitor is especially effective in downsizing a semiconductor device or the like.
The semiconductor integrated circuit may be formed over a single crystal semiconductor substrate such as a silicon wafer or may be formed over an insulating substrate by using a thin film transistor. In particular, in the case of forming the semiconductor integrated circuit over the insulating substrate by using the thin film transistor, the area of the semiconductor integrated circuit is larger than a circuit formed over a single crystal semiconductor substrate. Therefore, in the case of forming a semiconductor integrated circuit over an insulating substrate by using a thin film transistor, a structure in which the semiconductor integrated circuit is arranged so as to overlap with a coiled antenna is especially effective in downsizing a semiconductor device or the like.